5 AM is a good starting point, especially if the car is all packed and ready to go. I pack up the car the night before or wake about about 30 minutes before everyone else so the only thing we need to do is fill our cooler bag with ice packs and water bottles / snacks and we're off. We have three 9 year olds, so we have them sleep in their clothes the night before so there's no struggle with getting them dressed while they're groggy. We get them in the car and they usually fall right back asleep pretty quickly.
I'm looking at my notes from last year's trip (yeah, I keep journals of our vacations, because it's amazing how much one forgets...)
Remarkably, we didn't have to stop for our first bathroom break until the North Carolina welcome center right across the border of VA which was 6.5 hours in for us. For lunch, Exit 173 at Roanoke Rapids has tons of fast food options. There's a great app called iExit which can geolocate you, list upcoming exits and has listings of all the gas stations, restaurants, hotels, etc. at that exit. You can then select a place and launch your maps/direction app to navigate. It's really helpful. Chick-fil-a had a line out the door at lunch time, so we went to Arby's. So unless you're eating a late lunch or really want to wait forever for "fast" food, avoid Chick-fil-a lol
My wife took over driving after lunch and drove the next 5 hours until northern Georgia. I could tell she needed a break at that point, so I drove the rest of the way to Savannah. Part of the reason we drove to Savannah on day 1 was because we started last year's trip with 2 days at
LegoLand, which is farther south compared to WDW and we wanted to get there around noon. But I think on future trips we'll continue to stay over in Savannah so we can get to WDW earlier. Our first day is always a pool day and relax until our room is ready day, and getting to WDW earlier on Day 1 will make everyone happy (and might help avoid some of the inevitable traffic on I-4).
In any case, safe travels and enjoy the trip!